The right to bare arms has nothing to do with crime prevention or for protection from outside invasion.
The American 2nd Amendment has been cited many times as among the most ambiguous of all of the Amendments to their constitution. In one breath it seemingly begins by clarifying that it is addressing the issue to that of rules regarding Militias, an outdated and largely unremembered institution, and in the next suddenly seems to be talking about all people in general. This seems contradictory to many people and some believe that this opens the statement to interpretation. This, however, is not really so. The Amendment is actually quite clear and not contradictorily at all, it simply uses antiquated language to convey its message and it is from a lack of understanding of that language which causes ambiguity.
Hopefully I can help explain what is going on with the Amendment itself. I have my own opinion of whether the rights is contains are valid or not, but this is unimportant as long as one does not understand what the statement itself is actually talking about.
First, let's focus on the most confusing word in the sentence:
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
When these words were written, there was no such thing as a modern police force. The concept of the "police force" was a product of the industrial revolution and simply had not been invented yet at the time. Instead, the arm of the government meant to arrest people and hold them were the Militias, civilians called up by the government for the purpose of enforcing its laws. The institutionalization of militias into a uniformed law enforcement is where modern police come from.
Understanding that Militias at the time fulfilled the same role as police do today, it may be helpful to read the Amendment again with modern wording in place of its logical equivalent. To wit:
"A well regulated Police Force, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Now, let us focus on the second unclear portion of the wording. What does the word "regulated" mean? The word is still in common use today, particularly in terms of banks and corporations, but still its meaning had not changed much in the last 250 years. Regulation means, basically, "to restrict, control, or impose limiting rules upon." This makes sense because there is no such thing as regulating an industry by telling them "go nuts." Point of fact, the removing of rules against a body is known as "deregulation."
Understanding that Regulated, in this sense, means basically controlled or restrained, we can once again replace the outdated terminology in the sentence with a logical modern equivalent. To wit:
"A well restrained Police Force, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Now, in order to make sure that we are, in fact, not changing the meaning of the statement itself, we should check our interpretation against the historical background of the original statement. In 1791 the people of the American Colonies had, less than a decade before, just ended it's long struggle with it's own government. Until that time, they were not a separate country at all, but simply a collection of highly rebellious colonies. They had taken arms against their own government in an attempt to replace it with another, more local, one and had succeeded, much to the surprise of most observers. When it came time to write the rules of this new local unified government, among their highest priorities was to ensure that this new government be restrained in a way that they wished their previous government had been. Among these was the ability for the government to disarm its populace forcefully. Their Imperial government had attempted to evoke this right by seizing and destroying the civilian armory in Concord, Massachusetts, the defense of which became the opening battle of the war. Once the war was finished and the rules for their new government were being forged, there was widespread opposition to the creation of a constitution at all. The fear being that if the government were created and given powers over the people, then it would inevitably be abused in the same way. The Bill of Rights, in its entirety, was the response to that criticism, by codifying a list of regulations, ways in which the government could not use its power against its citizens. Among the first things they listed was the second amendment which addresses that exact issue.
People have a right to their own opinions, but they do not have a right to their own facts. Your opinion of whether or not people have the right to possess weapons is your own, but the meaning of the amendment itself is not in question.